This invention relates to pallets for use in transporting and storing goods. More particularly, the invention relates to twin sheet thermoformed plastic pallets having increased load handling capabilities.
Pallets have been constructed of various materials including wood, steel, and plastic. Wood pallets have problems of inadequate strength and limited life expectancy in use. Steel pallets, while having increased strength characteristics, are not suited to wet or corrosive environments. Both wood and steel pallets can be of considerable weight and neither are easily recycled, resulting in an additional cost for disposal at the end of their useful life.
Plastic pallets have been gaining increased acceptance due to factors such as the high strength to weight ratio, resistance to corrosion, and durability. While numerous techniques for producing plastic pallets are known, it has become increasingly popular to thermoform plastic pallets especially with the technique known as twin sheet thermoforming as discussed in U.S. Pat. Nos. 3,583,036 to Brown, 3,787,158 to Brown, and 3,925,140 to Brown.
Twin sheet plastic pallets are designed to take maximum advantage of the materials used. Efforts have been to maximize the load carrying capacity of the pallet, namely to meet its expected use by maximizing the load capacity for the given amount of material used in forming the pallet. The prior art contains pallets having linearly extending channels or ribs which are formed into the pallet to increase stiffness, see e.g. U.S. Pat. No. 3,187,691. These ribs or channels can have an undesirable effect of allowing bending or hinge moments to occur along the length of the rib, i.e. the material may flex about an axis determined by the length of the rib or channel. Attempts to counteract this have been to place parallel linear channels in one surface of the deck and a series of parallel channels running at an angle to the first series of channels in the lower surface of the deck, e.g. U.S. Pat. No. 3,610,173. Other efforts to increase the structural strength of the pallet have included use of non-linear protuberances or bosses formed in repeating symmetrical arrangements across the surface of the deck. The bosses do not have a substantially linear component in the surface of the deck and therefore no single boss makes a significant contribution to a bending or hinge moment across that single boss. See, e.g. U.S. Pat. No. 4,879,956.